(1) Field of the Invention
The present invention generally relates to a printing control apparatus in a page printer, and more particularly to a printing control apparatus by which a page printer can efficiently make prints.
(2) Description of Related Art
A page printer makes prints page by page. The page printer has a memory into which dot image information for one page is mapped, and an image having an accurate dot layout can be printed by the page printer. Thus, in the page printer, high quality prints can be made at a high speed. For a laser beam printer, an LED printer and a liquid crystal printer, each of which is a page printer which can be used personally, prices are particularly low.
In the page printer, the memory is provided with a plurality of bit map areas into each of which dot image information for one page is mapped to improve a printing speed. In this case, while dot image information stored in a bit map area is being printed out, dot image information of the next page is being mapped into the next bit map area by utilizing an otherwise idle time of a CPU.
In the above case where the memory is provided with a plurality of bit map areas each of which has a capacity of one page, it is necessary for the memory to have a large capacity. To decrease a capacity required for the bit map area in the memory, the following page printer has been proposed. In this conventional page printer, the memory is divided into a system area 1, a page descriptor area 2, a working area 3 and a bit map area 4, as shown in FIG. 1. Information used for controlling the printer is stored in the system area 1. The working area 3 is used for processing various information such as print data supplied from a host computer. The bit map area 4 has a capacity of one page or between one page and two pages. That is, the capacity of the bit map area is less than that of two pages. Print data supplied from a host computer is converted into descriptors each having an intermediate format so that dot image information corresponding to the print data can be easily mapped into the bit map area 4 based on the descriptors. That is, a time required for converting the descriptors into the dot image information is less than a time required for directly converting the print data supplied from the host computer into the dot image information. The descriptors are stored in the page descriptor area 2 in the memory. FIG. 2A indicates a bit map area 4 of one page. In a case where A4 sized image is printed at a rate of 240 dpi (dot per inch), the dot image information having 1872(width).times.2720(length) dots is mapped into the bit map area 4 of the memory. In this case, a bit map area 4 having a capacity of about 640K bytes is needed. In cases of B4 image size, the bit map area having a capacity of about 950K bytes is needed. In a case of A3 image size, the bit map area 4 having a capacity of about 1.2M bytes is needed. FIG. 2B indicates a bit map area 4 having a capacity between one page and two pages. In this case, the bit map area 4 is divided into a first area 4-1 of one page and a second area 4-2 of one page which are overlapped with each other so that an overlap area (O) is formed. In a case where the bit map has a capacity between one page and two pages, as shown in FIG. 2B, a printing control is carried out as follows.
In step 1, dot image information corresponding to one page printing data supplied from the host computer is mapped into the first area 4-1 of the bit map area 4 starting from an origin S1. In step 2, after the dot image information is completely mapped into the first area 4-1, all the dot image information in the first area 4-1 is shifted to the second area 4-2 of the bit map area 4 starting from an origin S2. In step 3, the dot image information is successively read out from the second area 4-2 of the bit map area 4 starting from the origin S2, and a print driving circuit is driven in accordance with the dot image information successively read out from the second area 4-2 of the bit map area 4 so that a print corresponding to the dot image information is formed on a recording sheet. While the print is being formed on the recording sheet in step 3, it is determined whether or not image information data in the overlap area (O) is finished being printed. In step 4, when it is determined that dot image information of the last line in the overlap area (O) is completely printed, since the first area 4-1 of the bit map area 4 is in an empty state, dot image information corresponding to the next page print data is mapped into the first area 4-1 starting from the origin S1. Then the above steps 1 through 4 are repeated a predetermined number of times corresponding to requested pages.
While the dot image information in the second area 4-2 is successively read out and printed on the recording sheet, in step 3, the next page print data is converted into descriptors and the descriptors are stored in the page descriptor area 2 in the memory. Then, in step 4, the dot image information is mapped into the first area 4-1 based on the descriptors corresponding to the next page's print data. Thus, the dot image information is easily and efficiently mapped into the first area 4-1. That is, the prints for a plurality pages can be formed at a high speed.
However, the above conventional process for forming prints in the page printer has the following disadvantages.
Immediately after an electric power supply of the page printer is turned on, and immediately after the prior job for forming prints is finished, the bit map area 4 of the memory is empty. In this state (herein after referred to as an idling state), even if the bit map area 4 is empty, the descriptors corresponding to the first page print data must be prepared and stored in the page descriptor area 2. After that, the dot image information is prepared based on the descriptors and mapped into the bit map area 4.
In this case, since immediate data such as the descriptors must be prepared before dot image information is mapped into the bit map area 4 although the bit map area 4 is empty, the mapping to form the first page is delayed. Particularly, in a case where the first page print data includes a large amount of images such as diagrams and graphs, an amount of data of the descriptors reaches a value in a range between few tens K bytes and few hundreds K bytes. That is, a large load for making the descriptors is applied to a processor in the page printer. As a result, it is further delayed to form the first page print. In addition, in a case where the first page print data includes many complex images, the capacity of the page descriptor area 2 of the memory becomes insufficient. In this case, since a process for converting the first page data into the descriptors is interrupted and the dot image information is formed directly based on the print data, a time for obtaining the descriptors is wasted.